Proposed experiments will examine the process of differentiation in neuroblastoma (C1300 murine) tumors formed by inoculation of cultured cells into A/J mice. Emphasis will be placed on the effects of the glucocorticoid dexamethasone and cyclic AMP-inducing agents (RO20-1724) on morphological and biochemical properties which are inducible within the tumor. These results will be compared to data obtained on cultured neuroblastoma cells. Morphological properties will be assessed by light and electron microscopy; biochemical properties by tyrosine hydroxylase activity, neurotransmitter (dopamine and norepinephrine) levels, and glucocorticoid receptor characterization. The ability of dexamethasone and other glucocorticoids to inhibit tumor occurrence or growth will measured. Results will determine whether induction of differentiation in vivo by dexamethasone occurs and whether therapy to induce differentiation could reduce the malignancy of neuroblastoma cells and thus could be a useful treatment modality.